(1) Field of the Invention
The invention relates to the field of measurement systems, such as optical measurement systems, e.g. systems for measurement spatial distributed physical properties by means of a sensor, e.g. an optical sensor.
The invention relates specifically to a method determining a physical property as a function of position based on the principle of frequency modulated continues wave (FMCW). In particular for a measurement system based on optical frequency domain reflectometry (OFDR).
(2) Description of Related Art
Typically a FMCW backscattering measurement system, such as an optical FMCW backscattering measurement system, comprises an excitation part, an evaluation part and a longitudinal extended sensor. For an optical FMCW system said sensor is typically an optical waveguide, typically an optical fiber, whereas for an electrical FMCW system a typical sensor is an electrical cable. The excitation part is adapted for exciting a series of frequency modulated signal in the sensor and the evaluation part then receives the response of the sensor to said signals, thus mapping the response as a function of frequency, which is referred to as the frequency data or the data in the frequency domain. Based on said response and a transformation from frequency domain to spatial domain one or more physical parameters of spatial distributed measurement points of the sensor along its length between the first and second end may be extracted.
A radar FMCW system may e.g. be used for determining distance to and velocity of an object. An optical FMCW backscattering measurement system may be applied to measure one or more physical parameters (typically temperature and/or strain) along an optical fiber. An electrical FMCW system may e.g. be used for monitoring the spatial distribution of temperature along an electrical cable, cf. e.g. EP-1 548 416.